In a typical liquid-developed electrophotographic imaging system (luminescent or conventional toner), as shown in FIG. 1, the imaging process includes the following steps.
First the electrostatic latent image is formed by uniformly charging a photoconductor (10), for example, a selenium plate, and then exposing (12) it to an image-wise pattern of radiation. The resulting voltage differential image is developed (14) with a liquid development electrode (as per U.S. Pat. No. 4,624,543) and then skived (15) (using either forced air or vacuum or both) to remove excess developer from the imaging plate. This toned image is then rinsed (16) and skived (17) with an inert hydrocarbon liquid, such as toner carrier liquid, to further remove excess developer. For applications in which the toner image is not transferred to another surface, the photoconductor imaging plate may then be blotted (18) to remove any excess drops from the edge of the plate by methods known to the art, and then dried (20).
In a preferred mode using luminescent toner, disclosed in commonly assigned U.S. Patent application Ser. No. 280,793, inventors Lubinsky and May, filed Dec. 7, 1988, the toned image is then scanned (22) with a beam of stimulating light generated by a laser. The laser beam is deflected by a galvanometer or polygon while the image plate is translated to effect a raster scan of the luminescent image. Light emitted from the image is collected and detected by a light collector of the type comprising a mirror box to collect the emitted light and direct it to a photomultiplier (PMT) or photodiode. A filter over the face of the detector blocks exciting radiation and passes emitted radiation. Examples of such a light collector/detector useful with this method are shown in U.S. Pat. No. 4,743,758 [Chan et al.] and U.S. Pat. No. 4,743,759 [Boutet].
The last cleaning step (24) in the process is to thoroughly remove all the toner from the imaging plate so that it can be reused. This last step is difficult since the electrostatic and VanderWaals type adhesive forces that hold the toner particles (diameter typically 0.4-1 .mu.m) to the surface require an aggressive cleaning procedure (e.g. mechanical squeegee, brush, skive, etc.) without generating scratches or digs on the surface of the imaging plate. When the toned image is dried, the difficulty in cleaning the plate is particularly enhanced because the drying process causes self-fixing of the toner image and increases the above adhesive forces. This last step ultimately determines the useful life of the photoconductor imaging plate.
Commonly assigned U.S. Patent Application Ser. No. 280,793, inventors Lubinsky and May, filed Dec. 7, 1988, discloses an electrographic process including the steps of forming a differential voltage pattern, developing the voltage pattern with luminescent toner, exciting the developed image to emit radiation, and photoelectrically detecting the emitted radiation to produce an electrical image signal.
U.S. Pat. No. 4,524,395, issued Jun. 18, 1985, inventor M. E. Banton discloses a multi-mode reproduction apparatus in which an image to be read is processed xerographically with dry toner to provide a developed image on a photoconductive member which is raster scanned with a high intensity beam. Light reflected from the photoconductive member is captured in an elongated rod-like collector and photoelectrically detected to produce an electrical image.
U.S. Pat. No. 4,204,725, issued May 27, 1980, inventors T. H. DiStefano et al., discloses a printer/copier having a sensing electrode which detects a charge change on a photoconductor surface as it is scanned with a laser beam.
U.S. Pat. No. 4,436,054, issued Mar. 13, 1984, inventors T. M. Ceelen et al., discloses a cleaning station for removing residual toner from a photoconductor. The cleaning station includes toner rolls for supplying cleaning liquid to flush toner particles from foam cleaning rolls.
U.S. Pat. No. 4,811,327, issued Mar. 7, 1989, inventors V. V. Petrov et al., discloses an optical storage device including a cylindrical information carrier disposed in a cylindrical container filled with transparent liquid or gaseous medium. The optical medium is scanned with a laser and read out by means of a photoelectric detector.
Commonly assigned U.S. Pat. No. 4,778,995, issued Oct. 18, 1988, inventors R. W. Kulpinski et al., discloses apparatus for reading out an image stored in a transparent stimulable phosphor sheet including means for maintaining a layer of optical index matching fluid between a light detector and the transparent stimulable phosphor sheet, to provide optical contact between the light detector and the transparent stimulable phosphor. Means are provided for scanning a beam of stimulating light in a line across the phosphor sheet and for relatively moving the phosphor sheet and light detector in a direction perpendicular to a scan line.
None of these patents discloses the photoelectric detection of a liquid-toned image through a liquid layer.